1. Field of the Invention
The invention pertains to the field of reliably receiving information for a computer. Such information can be received from a storage device or can be received from another computer communicating via a data communication protocol.
2. Description of Background Information
Prior art disk drives specify that they will deliver data to a computer with a reliability of at most one failure in about every 1013 blocks of data, wherein a block is typically 512 bytes. However, the prior art disk drives do not provide this level of reliability by reading a block only once. The drive may attempt to read the block multiple times as long as the overall throughput is not reduced significantly. It is estimated that as long as a drive reads a block no more than once every 105 blocks the throughput is degraded by less than one percent.
Prior art disk drives increase reliability by performing independent rereads. That is, when an uncorrectable error is detected on the first read, the first read is ignored and the block is reread. A mathematical analysis of such a scheme was given by Ara Patapoutian and Mathew Vea, xe2x80x9cThe Effect of a Reread on Data Reliabilityxe2x80x9d, IEEE Transactions on Magnetics, Vol. 33, No. 5, September 1997.
Another prior art rereading scheme was proposed in which two blocks are compared after data detection to find erasures, which in turn helps the ECC.
An embodiment of the invention is a method for increasing the reliability of a disk drive. A block of information is read from a storage medium to provide a first sample, which is stored. The method determines whether an uncorrectable error occurred during the reading, and when the error is determined to have occurred, the block of information is reread from the storage medium to provide a second sample. The first and the second sample are averaged to provide an averaged sample, and the averaged sample is decoded.
Another embodiment of the invention is a storage unit. The storage unit includes a reader for reading a block of information from a storage medium to provide a first sample and for storing said first sample. An error determining mechanism determines whether an uncorrectable error occurred during the reading and issues a command to the reader to re-read the block of information to provide a second sample when the uncorrectable error is determined. A processor receives and averages the first sample and the second sample and produces an averaged sample. A decoder decodes the averaged sample.